Virtual placeholder configuration for distributed input/output modules

ABSTRACT

A modular distributed I/O system for an industrial automation network that allows one or more modules of an island to be omitted without requiring reconfiguration of the system by maintaining a consistent I/O image representation of the distributed I/O network for various physical distributed I/O configurations, and managing reconfiguration changes using Virtual Placeholder objects.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.11/755,706, filed May 30, 2007, which application claims the benefit ofU.S. Provisional Application Nos. 60/809,855 and 60/809,856, both filedMay 30, 2006. This application is also related to U.S. PatentApplication Publication No. 2006/0268854, published Nov. 30, 2006. Allof these prior applications are hereby incorporated by reference intheir entirety.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

None.

TECHNICAL FIELD

The present invention generally relates to configuring modulardistributed I/O systems in industrial automation networks. Morespecifically, the present invention relates to a distributed I/O systemthat allows the user to maintain a consistent I/O image representationon a distributed I/O network for various physical distributed I/Oconfigurations having one or more I/O modules physically removed fromthe system.

BACKGROUND OF THE INVENTION

A programmable logic controller (PLC) is used to monitor input signalsfrom a variety of input points (i.e., input sensors) that report eventsand conditions occurring within a controlled process. For example, a PLCcan monitor such input conditions as motor speed, temperature, pressure,volumetric flow and the like. The PLC has a control program storedwithin its memory to instruct the PLC on what actions to take uponencountering particular input signals or conditions. In response tothese input signals provided by the input sensors, the PLC derives andgenerates output signals that are transmitted to control the process viaPLC output points to various output devices such as actuators andrelays. For example, an output signal can be provided by the PLC tospeed up or slow down a conveyer, rotate the arm of a robot, open orclose a relay, raise or lower temperature, as well as many otherpossible control functions.

The input and output points referred to above are typically associatedwith input modules and output modules, respectively. Input and outputmodules are collectively referred to as I/O modules herein. Thoseskilled in the art alternatively refer to such I/O modules as I/O cardsor I/O boards. I/O modules are typically adapted to be plugged intorespective slots located on a backplane board or other attachment systemprovided by the PLC. The slots are coupled together by a main bus thatcouples any I/O module plugged into the slots to a central processingunit (CPU). The CPU itself can be located on a card that is adapted tobe plugged into a dedicated slot on the backplane board of the PLC.

In many control systems, PLCs are arranged in a master/slave networkthat includes a master PLC and a plurality of remote slave units thatcan include other PLCs or devices. In this type of a network, the masterPLC controls its own I/O connection points and also the respective I/Oconnection points for the remote slave unit(s). The control commandsfrom the master PLC are derived from data obtained from the remote slaveunits, which is obtained from the I/O module(s) connected to each remoteslave unit.

To meet the needs of machine manufacturers and users, automationarchitectures have been decentralized or distributed while deliveringperformance comparable to centralized systems. For instance, theADVANTYS STB distributed. PO system is an open, modular input/outputsystem that makes it possible to design islands of automation managed bya master controller via a bus or communication network. The ADVANTYS STBdistributed I/O system is a product of Schneider Automation Inc., OneHigh Street, North Andover, Mass.

These automation islands, typically installed close to the machine, helpreduce the time and cable cost for sensors and actuators, whileincreasing system availability. The island components are electronicmodules mounted on one or more DIN rails (i.e., standardized rails).These clusters of modules, known as segments, carry a bus from thebeginning to the end of each island. The island bus provides powerdistribution, signal sensing, and power management to compatiblemodules.

An island can include one or more segments comprising a networkinterface module (NIM), a power distribution module (PDM), andadditional modules for various architectures such as I/O modules, busextension modules, island bus termination, and island bus extensions.

The island is typically configured using a user interface. The NIM isresponsible for assigning addresses to the I/O modules and formaintaining a process image of the I/O modules. Both the NIM and the I/Omodules participate in I/O modules automatically obtaining theiraddresses based on their relative physical locations—using anauto-addressing protocol. The NIM is responsible for maintaining aprocess image of the I/O modules, which is based on the addresses of theI/O modules. Such an addressing scheme could not handle the situationwhere a user wanted to physically remove I/O modules that correspond tounwanted options without changing the program to add/delete the options.

Each island is comprised of several I/O modules, divided into severalgroups. Each group of I/O modules represents one option available in acustomer's machine. When all options are included in a particularmachine, then all groups of I/O modules must be physically present; thisforms the “base” configuration. Different machines may contain differentoptions, hence different groups of I/O modules.

When a machine is built, a technician uses a human-machine interface(HMI) connected to the PLC that controls the automation system and otherparts of the machine to select which options are physically present inthe machine. To ease PLC programming, the process image of the islandmust remain identical, regardless of the machine options that are chosenby the customer (and subsequently the I/O modules that are physicallypresent).

In prior versions of automation systems, the Customer must build andmaintain different island configuration files for machines withdifferent options; this can be quite burdensome in cases where there aremany combinations of machine options available. It is desired that foreach base configuration, only one island configuration be necessary.

The present invention provides an I/O configuration solution to overcomethese and other problems.

SUMMARY OF THE INVENTION

The present invention is directed to an improved distributed I/O systemthat allows the user to create one fully defined process image thatcontains all the I/O modules needed for all the desired configurationsof the physical distributed I/O island using Virtual Placeholderobjects. This allows one or more I/O modules to be removed withoutrequiring reconfiguration or reprogramming of the system. By maintainingthe identical process image of the island, a user does not need toreconfigure or change the PLC program, even if the user removes certainmodules from the base set.

One embodiment of the present invention is directed to an automationsystem comprising: a network interface module; a plurality of I/Omodules comprising an I/O island; and a translation table configuredusing Virtual Placeholders such that an I/O module in a physical slot Xhaving node ID X is presented outside the I/O island as if that I/Omodule were located in slot Y.

Another embodiment of the present invention is directed to a system forconfiguring a process image in an automation network having one or moreoptionally uninstalled I/O modules, the system comprising: an islandhaving a network interface module, the island further including aplurality of connections for I/O modules; and configuration software runby the network interface module that provides a consistent process imagefor each one of the plurality I/O modules whether or not physicallypresent.

Still another embodiment of the present invention is directed to amethod of configuring a process image of an island to indicateoptionally uninstalled I/O modules, comprising the steps of: providingan island having a network interface module and a plurality of ports,each of the plurality of ports capable of connection to an I/O module;connecting I/O modules to select ports of the plurality of ports; andcreating a process image of the island that indicates whether an I/Omodule is physically present and not present using Virtual Placeholders.

The present invention is particularly useful for a user who builds manysystems and/or machines with I/O configurations that differ (from aremote I/O point of view) only in the number and types of I/O modulesphysically present. In the past, each of the configurations of I/Omodules would result in a change to the I/O image representation on theremote I/O network, necessitating a change to the master controllerprogram to accommodate the configuration change. The present inventionfacilitates keeping the I/O image representation the same for thevarious configurations.

The configuration software of the present invention is adapted todescribe the master (maximum) remote I/O configuration. The software isthen used to identify those I/O modules that will not be present in theactual physical configuration to create a reduced configuration. Thephysical remote I/O configuration is built without the “not-present”module(s). The reduced or de-populated configuration is applied to thephysical configuration, which maintains the same I/O imagerepresentation on the remote I/O network as the master configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the present invention will be apparentfrom the following specification taken in conjunction with the followingdrawings.

FIG. 1 (PRIOR ART) is a simplified block diagram of a typical automationcontrol system or network having a distributed I/O system or island;

FIG. 2 is an elevation view of a distributed I/O system or island inaccordance with the present invention;

FIG. 3 is a main display screen of the configuration software forconfiguring the distributed I/O system or island shown in FIG. 2;

FIG. 4 is a general display screen for configuration of an I/O modulewithin the distributed I/O system or island of FIG. 2;

FIG. 5 is an options display screen for configuration of the I/O module,showing the module “Not Present” option;

FIG. 6 is a partial display of the main screen similar that of FIG. 3,showing those modules configured to be not physically present beingindicated as so;

FIG. 7 is a flowchart showing the steps a user would take to configurean island using the Virtual Placeholder feature of the invention; and

FIGS. 8A-8D are routing diagrams showing the various data mapping andstatus mapping configurations used in a simple example of the invention.

DETAILED DESCRIPTION

While this invention is susceptible of embodiments in many differentforms, there is shown in the drawings and will be described in detailherein a preferred embodiment of the present invention with theunderstanding that the present disclosure is to be considered as anexemplification of the principles of the invention and is not intendedto limit the broad aspect of the present invention to the embodimentillustrated.

FIG. 1 depicts a typical automation control network or system 110 havinga distributed I/O system (i.e., island). The automation system 110includes a local area network 112, a host computer 114, at least onemaster or main programmable logic controller (PLC) 116, a distributedI/O system or island 118, a human-machine interface (HMI) terminal 120,other network nodes 122, and other slave PLCs 124. The distributed. I/Osystem 118 includes a network interface module (NIM) 126, a powerdistribution module (PDM) 128, and I/O modules 130. As will be describedbelow in detail, configuration software provides display screens on thehost computer monitor 132.

The local area network (LAN) 112 can be Ethernet based (e.g., IEEE802.3) or can use other protocols such as, but not limited to, CANopen,Profibus, FIPIO or the like. Furthermore, the network 112 can be wiredor wireless (e.g., IEEE 802.11 or the like).

The master or main PLC 116, like the host computer, is operativelyconnected to the local area network 112. As will be appreciated by thosehaving skill in the art, both the host computer 114 and the main PLC 116can be conventional products that are currently available in themarketplace.

The host computer 114 is operatively connected to the master or mainprogrammable logic controller 116 via the LAN 112. In operation, thehost computer 114 provides the master or main programmable logiccontroller 116 with data or programming that represents a desiredoperation or function to be performed by the control network 110. Thedata can be based, at least in part, on modules (i.e., options), whilebuilding the process image as if all modules are present.

Turning now to FIG. 2, an elevation view of a distributed I/O system orisland 218 in accordance with the present invention is depicted. Thedistributed I/O system or island can be used within the control networkdepicted in FIG. 1. As indicated previously, the control network 110includes, but is not limited to, a local area network 112 having a hostcomputer 114 and at least one master or main programmable logiccontroller (PLC) 116 connected thereto. Additionally, the distributedI/O system 218 is connected to the local area control network 112. Theisland 218 has a network interface module (NIM) 226, a powerdistribution module (PDM) 228, and a plurality of I/O modules 230.

As will be described in detail below, the island 218 of FIG. 2 isconfigured using a user interface (i.e., the host computer 114) having asoftware interface installed thereon. The host computer. 114 suppliesthe island 218 with configuration data or programming. In particular, aconfiguration program is loaded onto the host computer 114 where, byexecuting the program, a user can configure the island 218.

The I/O devices or modules 230 that can be attached to the island 218include, for example, input sensors and/or output actuators. The inputsensors can be for a variety of variables including, but not limited to,temperature, flow, pressure, speed, and the like.

FIG. 3 is a main display screen 300 of the configuration software forconfiguring the distributed I/O system or island shown in FIG. 2. Asshown in FIG. 3, the configuration software provides a main displayscreen on the host computer monitor 132. The main screen 300 includesseveral windows and components.

A Workspace Browser 310 displays the contents of the currently openworkspace in a hierarchical or tree-structured fashion. The browserdisplays all the islands currently residing in the selected workspace.

An Island Editor 320 provides a graphical representation of the logicalislands being configured with the software. Each opened logical islandhas its own Island Editor window pane 325.

A Catalog Browser 330 is a list of all the modules available to the userwhen assembling an Island. The catalog is displayed as a tree structurein which various modules are grouped according to type.

A Log Window 340 displays the results of any operation performed by theconfiguration software. In Online mode, it displays additionally healthinformation of the physical island including upstream fieldbus errormessages.

A Status Bar 350 and Status Indicators 360 at the bottom of the screenprovides status messages, offline/online status, physical island status,etc. Two Status LEDs 370 at the top-right side of the screen are activewhen the software is in online mode. The green LED represents the RUNLED on a NIM, while the red LED represents the ERROR LED. Several blinkcodes are also used to indicate various island states of operation.

FIG. 4 is a general display screen for configuring an individual I/Omodule. The Module Editor screen provides information about a selectedmodule, allows the user to modify some operating parameters, and permitsthe user to view live I/O data when the software is in online mode. TheModule Editor is invoked by selecting the appropriate module from theIsland Editor or from the Workspace Browser.

The General tab 400 of the Module Editor displays descriptiveinformation about the selected module. All information on this tab isread-only. The name of the module and its exact location on the islandbus are displayed in the title bar at the top of the screen. The generalinformation provided includes the module name, vendor code, vendor name,version, and a brief functional description of the module.

FIG. 5 shows the Options tab 500 for configuration of the I/O module.This window provides the user the ability to configure the module as a“Mandatory Module” 512 or as “Not Present” 514. If the user designatesthe selected I/O module as Mandatory by selecting checkbox 512, and theMandatory Module fails or is removed from the island, the entire islandbus switches to pre-operational mode and the island bus stops.

If the user designates the selected I/O module as “Not Present” byselecting checkbox 514, the module is marked using the VirtualPlaceholder feature of the present invention. A Virtual Placeholderallows the user to remove certain physical island I/O modules from abase configuration, while keeping the identical process image. Thisallows one to define an island with various options removed withoutchanging the PLC program which controls the island. In the case ofhaving removed some I/O modules, the remaining ones may have to bephysically plugged next to each other, as spare slots are sometimes notallowed.

According to a preferred embodiment of the present invention, the island218 maintains the same process image after a module is configured to be“Not-Present” and physically removed from a base set of modules for theisland. Accordingly, by maintaining the process image, a user is able tooperate the same configuration and program without being required tochange the configuration or program in the PLC 116. Hence, the userchooses the modules that the user does not wish to physically install,but will still take up space in the process image to maintain the sameprocess image as the original full system.

If no module is selected to be “Not Present,” then the existingauto-addressing protocol is used. However, if a user selects one or moreI/O modules not to be present, then the use of an amendedauto-addressing protocol may be required. An auto-addressing protocol isprovided in a network interface module and an I/O module for skippingnode ID's of uninstalled modules not to be used in the process. Eachtime that the island is powered up or reset, the NIM automaticallyassigns a unique island bus address to each module on the island thatwill engage in data exchange. Refer to U.S. Patent ApplicationPublication No. US 2006/0268854 A1 for a detailed description of thepreferred auto-addressing protocol.

FIG. 6 is a partial display 600 of the main display screen similar thatof FIG. 3, showing those modules configured to be Virtual Placeholders(and not physically present) being designated with indicia 612 showingtheir absence. In the preferred embodiment, the Module Editor marks allthe Virtual Placeholder modules with crossed red lines over the view ofthe particular module to indicate that the module is not physicallyinstalled.

Thus, instead of the full configuration, a user may build a physicalsystem that only includes the following modules shown in FIG. 6: theNetwork Interface Module 626, such as the ADVANTYS STB NCO 2212; thePower Distribution Module 628, such as the ADVANTYS STB PDT 3100; aDigital Output Module 632, such as the ADVANTYS STB DDO 3200; and anAnalog Output Module 640, such as the ADVANTYS AVO 1255. Accordingly,only two ADVANTYS I/O modules are physically installed. Modules 630,634, 636, and 638 are shown in FIG. 6 as Virtual Placeholders.

It is important to distinguish between a “physical island” and a“logical island”. A “physical island” is an assembly of distributed I/O,power distribution, and island bus communication/extension modules thatfunction together as one node on a fieldbus. An island contains up to 32I/O modules plus a NIM, one or more power distribution modules, andoptionally some modules that let you extend the bus to multiple segments(or rails) of other I/O and to standard CANopen devices. Using thepresent invention, the configuration software lets the user model aphysical island so that it can be tested against design rules andcustomized to meet application requirements. This software model iscalled the “logical island”. As the user develops a logical island, thesoftware will provide warnings about any mistakes made in the model, andit will usually prevent the user from creating an invalid configuration.For example, it prevents you from placing a DC module in a locationwhere it would receive AC field power (and vice versa). The logicalisland is a file in the software program with a “.isl” extension. Itcontains a description of the physical island, including all the moduleson the island and all the operating parameters associated with eachmodule that may be defined in software. Hence, the logical view of theisland which reflects the I/O map for the user program remainsunchanged, while the physical view which reflects the physically presentSTB modules may change. In case of having removed some modules, theremaining ones may have to be physically plugged in next to each other,as some system buses may not allow spare slots.

FIG. 7 is a flowchart 700 showing the general steps that occur when auser configures an island using the Virtual Placeholder feature of theinvention.

Starting with Step 710, the user would use the configuration software tobuild a new island. In this simplified example, only three modules areused for the sake of clarity. Initially, the first module has an address1, the second module has an address 2, and the third module has anaddress 3.

In Step 720, the user chooses which modules that he does not wish tophysically install, but still take up space in the process image (tomaintain the same process image as the original full system). As shownabove in FIG. 5, the selection process is done using the VirtualPlaceholder “Not Present” checkbox 514 in the Options tab 500 of the I/Omodule configuration software. The modules selected to not be physicallypresent are displayed with indicia 612 indicating their absence, asshown by the crossed red lines in FIG. 6. The user would then physicallyremove the Not Present module(s). In this simplified example, only the2nd module would be a Virtual Placeholder and removed from the physicalsetup.

In Step 730, the logical addresses of the modules are now automaticallydetermined by the configuration software. The first physical moduleretains its logical address 1, but the second physical module, whichused to be third module, is now reassigned to logical address 2.

This logical address information is internally stored by theconfiguration software in Step 740 in object XXYYh as follows: logicalnode address of physical node 1=1; logical node address of physical node2=3; logical node address of physical node 3=null. In the preferredembodiment, a new object index is used as an address translation tableto show the correlation between the logical node address of and thephysical node address when the Virtual Placeholder feature is enabled.The new object XXYYh and any extended objects become part of theconfiguration data, which are saved in flash memory.

In Step 750, the translation table generated by the configurationsoftware is downloaded to the network interface module as part of theconfiguration data. Depending upon the configuration tool used, thetranslation table must be downloaded first, and then the other objectdictionary entries should to be downloaded.

Step 760 illustrates that the data packet from each node is “rerouted”to the location corresponding to the logical address for that module. Inthe preferred embodiment, this is done by changing the “COB-ID” (CANObject Identifier) of the data packet of those modules whose logicaladdress no longer matches the physical address. This “Data Mapping” Step760 will be described below in FIGS. 8A and 8B.

A similar procedure is used for the error registers in Step 770. Again,the logical address of each physical module (using object XXYYh) is usedto signify which node is in error. This “Error Status” Step 770 will bedescribed below in FIGS. 8C and 8D.

After the NIM has powered up and the new configuration has beendownloaded, the island state is displayed in the configuration softwareand can be sent to the fieldbus master, wherein only those I/O modulesthat are selected to be physically present are taken into account. Inthis example, if both the first and third I/O modules are present andfunction normally, the island state will not present an error messageindicating that unexpected or missing modules are in the islandconfiguration. Under prior auto-addressing protocols, the node ID'swould have had to been node ID 1 and node ID 2. Selecting the VirtualPlaceholder option causes the module to be taken out of theauto-addressing, identification check, configuration, and diagnosticsprocedures of the NIM. The module configuration data is still part ofthe island configuration. The I/O image of the island remains unchanged,i.e., it still contains the I/O data of the module.

FIGS. 8A-8D are routing diagrams showing the various data mapping andstatus mapping configurations used in the three-module example of FIG.7.

In FIG. 8A, the normal data memory mapping is shown when the VirtualPlaceholder is not used, i.e., all I/O modules are physically present.As shown in the Figure, there would simply be a direct one-to-onecorrespondence between the physical node IDs and the logical node IDsstored in the NIM.

FIG. 8B shows the Virtual Placeholder data memory mapping when thesecond module is removed and marked “Not Present”. Since the secondmodule was removed (and the third module shifted left into its place atphysical node 2), then physical node 1 is mapped to logical node address1, physical node 2 is mapped to logical node address 3, and physicalnode 3 has a “null” logical node address. This data mapping isaccomplished in the translation table stored in object XXYYh.

A correspondence similar to FIG. 8A is shown in FIG. 8C for normalstatus memory mapping when the Virtual Placeholder is not used, i.e.,when all I/O modules are physically present. As before, there wouldsimply be a direct one-to-one relationship for the error messages sentfrom the physical node IDs to the status memory locations for thelogical node IDs stored in the NIM.

However, FIG. 8D illustrates that when the second module is removed andmarked “Not Present”, the translation table stored in object XXYYhroutes the error messages from physical node 1 to logical node address1, and from physical node 2 to logical node address 3. Since the secondmodule was removed (and the third module shifted left into its place atphysical node 2), then the third module has a “null” logical nodeaddress.

Hence, it can now be understood that the island configuration softwareincludes a translation table that informs the system which physicallypresent node corresponds to which logical node, and translates thephysical view to the logical view every time it gets a physicalreference. This translation table is generated by the configurationsoftware and is downloaded and stored in the NIM as part of theconfiguration data. Other configuration data to be downloaded to the NIMremains unchanged

Those skilled in the art will appreciate that the NIM firmware needs tobe modified in a way that it will be able to handle the physical andlogical view as described above. The NIM interfaces (command interface,diagnostic interface, process image) will always present the logicalview. Therefore, the upstream fieldbus will also represent the logicalview without (or with minor) changes in the existing fieldbus handler.

The Virtual Placeholder feature may be limited to certain I/O modulescapable of being part of the auto-addressing. The other(non-auto-addressed) modules may not be allowed to be “Not Present”.

In summary, the Virtual Placeholder feature lets the create a standardisland configuration and de-populated variations of that configurationthat share the same fieldbus process image, thereby maintaining aconsistent PLC or fieldbus master program for various islandconfigurations. In other words, using the Virtual Placeholder feature ofthe present invention, an I/O module in a physical slot X (node ID X) ispresented to the outside world as if it were located in slot Y, similarto using an alias.

This Virtual Placeholder capability allows a user to create a master(maximum) configuration of I/O modules that can be de-populated to formsubsets (both in number of I/O modules and features), yet retain thesame I/O image representation on the remote I/O network. One suchapplication is that of a machine builder who builds machines withseveral options that can be specified by the end-user. By properlyportioning his system into various options, he can create machines withparticular features that exist if particular options (of I/O modules)are present, or without those particular features if the options are notphysically present, without changing the master controller program withregards to addressing the I/O image. The de-populated islands arephysically built using only those modules that are not marked as beingnot present, thus saving cost and space.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and have been described in detail. It should be understood,however, that the intention is not to limit the invention to theparticular embodiments described. To the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

The invention claimed is:
 1. A system for configuring a process image inan automation network, the system comprising: a physical island having anetwork interface module, the physical island further including aplurality of input/output (I/O) modules, wherein configuration softwarerun by the network interface module maintains a consistent process imagefor various distributed I/O configurations having one or more I/Omodules of the plurality of I/O modules physically removed from thesystem using virtual placeholders, and wherein said configurationsoftware generates a translation table that provides a correlationbetween node addresses of the physical island and node addresses of alogical island model of said physical island, wherein an I/O module ofthe plurality of I/O modules in a physical slot X having node ID X ispresented outside the physical island as if that I/O module were locatedin slot Y.
 2. A method of configuring a process image of a physicalisland, the method comprising: providing the physical island having anetwork interface module and a plurality of ports, each of the pluralityof ports capable of connection to one of a plurality of input/output(I/O) modules; connecting at least one of the plurality of I/O modulesto at least one of the plurality of ports; and, creating the processimage of the physical island that indicates whether each of theplurality of I/O modules is physically present and not present usingvirtual placeholders, wherein the creating the process image furtherincludes generating a translation table that provides a correlationbetween node addresses of the physical island and node addresses of alogical island model of said physical island, wherein an I/O module ofthe plurality of I/O modules in a physical slot X having node ID Xappears in the logical island model as if that I/O module were locatedin slot Y and wherein an I/O configuration of the physical islandmaintains a consistent process image for various physical distributedI/O configurations having one or more I/O modules of the plurality ofI/O modules physically removed.
 3. The system of claim 1, wherein saidconfiguration software provides for an indication of one or more I/Omodules of the plurality of I/O modules selected by a user to bephysically not present in the physical island to be displayed withparticular indicia indicating an absence, such that the one or more I/Omodules indicated as being physically not present are distinguishablefrom other I/O modules indicated as being physically present.
 4. Thesystem of claim 1, wherein said configuration software provides a userwith functionality to create the logical island model of said pluralityof I/O modules comprising the physical island, such that the logicalisland model can be tested against particular design rules andapplication requirements.
 5. The system of claim 4, wherein saidtranslation table is downloaded and stored in said network interfacemodule as part of configuration data.
 6. The method of claim 2, whereinthe creating the process image includes: (a) creating the logical islandmodel using the virtual placeholders, and (b) determining the logicalnode addresses for each of the plurality of I/O modules.
 7. The methodof claim 2, further comprising: providing for an indication of one ormore I/O modules of the plurality of I/O modules selected by a user tobe physically not present in the physical island to be displayed withparticular indicia indicating an absence, such that the one or more I/Omodules indicated as being physically not present are distinguishablefrom other I/O modules indicated as being physically present.
 8. Themethod of claim 2, wherein the creating the process image includesdetermining the logical node addresses for each of the plurality of I/Omodules.
 9. A non-transitory computer-readable storage medium havingcomputer-executable program instructions stored thereon that whenexecuted by a processor, cause the processor to perform a methodcomprising: providing a physical island having a network interfacemodule and a plurality of ports, each of the plurality of ports capableof connection to one of a plurality of input/output (I/O) modules;connecting at least one of the plurality of I/O modules to at least oneof the plurality of ports; and, creating a process image of the physicalisland that indicates whether each of the plurality of I/O modules isphysically present and not present using virtual placeholders, whereinthe creating the process image further includes generating a translationtable that provides a correlation between node addresses of the physicalisland and node addresses of a logical island model of said physicalisland, wherein an I/O module of the plurality of I/O modules in aphysical slot X having node ID X appears in the logical island model asif that I/O module were located in slot Y and wherein an I/Oconfiguration of the physical island maintains a consistent processimage for various physical distributed I/O configurations having one ormore I/O modules of the plurality of I/O modules physically removed. 10.The non-transitory computer-readable storage medium of claim 9, whereinthe translation table is downloaded to the network interface module. 11.The non-transitory computer-readable storage medium of claim 9, whereinthe processor further performs: routing error messages to apredetermined logical address based on the virtual placeholders.
 12. Thenon-transitory computer-readable storage medium of claim 9, wherein thecreating the process image includes determining the logical nodeaddresses for each of the plurality of I/O modules.
 13. Thenon-transitory computer-readable storage medium of claim 9, wherein theprocessor further performs: providing for an indication of one or moreI/O modules of the plurality of I/O modules selected by a user to bephysically not present in the physical island to be displayed withparticular indicia indicating an absence, such that the one or more I/Omodules indicated as being physically not present are distinguishablefrom other I/O modules indicated as being physically present.
 14. Thenon-transitory computer-readable storage medium of claim 9, wherein thecreating the process image includes: (a) creating the logical islandmodel using the virtual placeholders, and (b) determining the logicalnode addresses for each of the plurality of I/O modules.